A direct conversion receiver down converts a radio-frequency to a baseband. The baseband signal is then generally filtered using an analog filter to suppress unwanted signal components such as adjacent channels and/or the like. However, in use, an analog-baseband filter (analog filter) may cause unwanted distortion to a signal (e.g. amplitude ripple, group delay ripple and/or the like). A digital equalizer may be used to compensate for unwanted distortion introduced by the analog filter.
In some cases an analog filter is constructed using electronic components such as resistors and capacitors on an integrated circuit. Each of these components may be manufactured with a certain tolerance caused by variations of the semiconductor process. For example, a value, such as a time constant, that is formed by a resistor and a capacitor may vary by 30% or more between production batches, over temperature and even between samples of the same circuit that are located differently on a silicon wafer during the production process. In comparison, telecommunication standards such as long term evolution (LTE), Wideband Code Division Multiple Access (WCDMA) and/or Global System for Mobile Communications (GSM), for example, impose strict limits on signal quality. Typically, the error on the signal must be kept well below 1% at any processing stage. To meet the requirements of communication standards and to obtain a functional device in general, it is necessary to calibrate components during operation of the device. For example, calibration may take place every time the device is turned on, or every time a channel is switched.
A number of methods have been proposed in an effort to provide some characterization of the mismatch of analog component values with very high accuracy. However the proposals have generally suffered from various drawbacks including, for example, implementation limitations that do not allow for correction of filter parameters with the same accuracy (e.g. required number of control bits becomes impracticable).